TEA TECHNOLOGY

Introduction
 Tea comes from the bush plant, Camellia sinensis
 Has been used as beverage for years since then.
 Accidentally discovered in China (<5000 years when a leaf dropped inside cup of water and
developed a pleasant taste, flavour and colour. Just like saccharine?
 Cultivation:
i. started in India (1818-34)
ii. Java 1824
iii. Ceylon (Srilanka) 1867
iv. Durban in botanical gardens (1850)
v. Malawi 1878
vi. Kenya (1900/3 in Endebbes and Limuru)
 Commercial development started in 1920-30
 Kenya now is leading in production after India and Srilanka.
 Much of China’s production is consumed locally.
 USSR also has some tea (USSR-Russia)

 Kenyan tea industry is divided into 2.

1. Large scale farm (Estates) production (40%)e.g.
Company No of factories
Unilever Tea (K) Ltd 11
Eastern produce 7
George Williamson 3
 Sotik Tea Co. 1
Kikebe Ltd 1
Kaisugu 1
Nandi Tea 1
Sotik Highlands 1
Keritor Ltd 1
Tinderet Tea Ltd 1
Kaisagat Tea Factory 1
Kiptagit Tea Factory 1
Ceres Tea Estate 1
James finlays-4 factories
 These are much more productive in Yields/ha as they allow plucking of >2 leaves and buds
which also compromises quality.

2. Small holders -60% under auspiceof KTDA-

http://www.ktdateas.com/index.php.
 The factories are owned by farmers but managed by KTDA agency:
o advice on production at farms
o harvesting, handling,
o Processing and marketing.
 Mission and vision of KTDA:
Mission:
To invest in tea and other related profitable ventures for the benefit of the shareholders and
other stakeholders
Vision:
To be the preferred investment vehicle for the small holder tea farmers in Eastern Africa
 Have good quality tea (allows only 2 leaves and buds to be plucked).
 Mainly deal with black CTC and black orthodox tea
 Factories based on 7 regions: Aberdare ranges-2, Mt. Kenya-2, Kisii, Nandi, Kericho,
 N/B:
o There is a Kenya tea directorate under AFA
o License tea processing factories
o Promote Kenyan tea at all levels
o Disseminates information related to tea
o Policy advice to government.
Chemical constituents of tea leaf (soluble substances)
Substance Percent dry Percent total
weight soluble solids black tea

Fresh Black
shoot tea

1. flavanol (quality)
i). EGCG (epigallocatechin 9-13 1-3 3-8
gallate)

ii). ECG (epicatechin gallate) 3-6 These are polyphenols

which are derivatives of gallic or
iii). EGC (epigallocatechin) 3-6
catechin e.g tannins
iv). EC (epicatechin) 1-3
v). Others 1-2
2. Flavonols and their 3-4 2-3 6-8
glycosides

3. Flavandiols 2-3 - -
4. Phenolic acids and 5 4 -
depsides

5. Thioflavins (if high then - 1-2 3-6

high quality tea)

6. Dialyzable biflavonols - 2-4 6-10

and dialyzable thearubins

7. Non-dialysable materials- - 1-2 3-5

thearubigins

8. Polysaccharides 14 14 3-4
9. Proteins 15 15 0.5-1
10. Caffeine 3-4 3-4 8-11
11. Amino acids and 4 5 14
peptides

12. Sugars 4 4 11
13. Organic acids 0.5 0.5 1.5
14. Mineral substance 5 5 10
15. Volatile substance 0.01 0.02 0.05
N/B: Thearubigins formed by fermentation contribute to the primary quality black tea but fermentation
for too long tends to increase them at the expense of theaflavins.

Factors affecting composition of tea

The tea composition is synonymous to tea leaf
a) Genotype characteristics
 The two extreme gynotype are Camellia assamica and Camellia sinensis. There are also
intermediates between the two.
 The chemical composition of shoots differ
 Flavanol content in assamica (30%) sinensis (10%)
 The proportions of individual flavanols differ with assamica containing high
proportion of gallate esters than sinensis.
 Flavanol- present largely as mono and diglycosides in assamica while trad.
Triglycerides in high proportions in sinensis
 Volatile fraction- proportionately large quantities of relatively high boiling
terpenoids and aromatics substances generally considered responsible for
desirable flavouring characteristics in sinensis.
 In summary- While assamica has generally large leaves, high yields and rich in
flavanols and caffeine of which are responsible for colour, strength and briskness,
sinensis are superior in certain flavour characteristics.
b) Environment
i) Cultural practice
 Age:
 Yields and quality potentials of tea bush not fully realised till 10 years after
planting.
 Economic importance of tea bushes generally 40-45 years but may be larger if
maintained.
 In the first 10 years quality is not fully developed but in remaining years quality
potential fully realised.
 Pruning:

- Most important cultural practice.

- Kenya’s pruning cycle 3-4 years to keep bushes at manageable heights

- Also to keep plant in vegetative phase.

- Difference in quality can be detected according to time elapsed since last pruning.

- Stimulates young shoots constitute cropped proportions.

- After pruning the quality increases with time.

- Renew actively growing branches for replacement
 - The 4 types of pruning include;
a) Collar pruning (near the ground )
b) Medium pruning
c) Top pruning
d) Fringe or lung pruning
 Shade (shading of tea)
o Has effect on the under growth.
o Depending on the climate provided in form of the shades to protect from
relative high temperatures.
o Shade trees were removed because of reduced yields but the effect of shade
on tea quality not very clear.
o There has been conflicting results.
 Fertilizers
Application may affect quality.
K fertilizers have little effect on quality.
 PO s improves quality (vary with district. But these are not usually used because they
4

do not sufficiently increase yields.

 Nitrogenous fertilizers commonly used increases yields considerably and studies show
increase in Nitrogen rates reduces the quality of made black tea and reduced flavanol
levels. The flavour decreases and thus low quality final made tea.
ii. Altitude
 In high altitude, tea universally regarded as superior to low one
 Considered to have important effect particularly on volatile fractions.
iii. Climate
 Temperature, light, humidity, day length (not much of a problem because do not vary much in
Kenya)
 Best quality associated with slow growth of tea bush.
 If unfavourable climatic conditions ( less relative humidity) low yields but high quality
c) Harvesting
i) Plucking standards
 70-90 days for another plucking.
 Size of harvested shoot or the plucking standards influence quality.
 Best tea determined by plucking only 2 terminal leaves and bud (fine plucking).
 Course plucking- 3 or more leaves below the apical bud.
 Caffeine content decreases with maturity thus high caffeine content only produced by fine
plucking standards
 Also the theaflavin value decreases as plucking become course.

ii) Handling leaf

 Avoid damage after plucking or overheating leaf to maintain quality.
 Pluckers to use basket sacks, after weighing and collection leaves should be transported with open
sacks or baskets rather than bulking in lorry or trailers
 This helps prevent overheating damage which will initiate chemical reaction that will change the
composition of tea leaves.

TEA PROCESSING
 Quality control and tasting ensures quality of final product of delivered tea leaf.
 Various tests reject consignment, downgrade or carry out sorting.
 The 3 products of tea processing are,
Black tea or orthodox fermented dried
Green tea-unfermented
Oolong tea-partially fermented
- Black tea differs from green tea in that during fermentation stage black tea is fully fermented while
green tea is not.
- The enzymes responsible for fermentation are inactivated after maceration hence maintains the
chlorophyll.
- Oolong tea is between the black and green tea. There is potential fermentation of macerated tea leaves
before drying.

BOILER
AIR
GREEN LEAF. TA=81% CN=10%

Temps< 350c

AT 90-
16-20hrs
For Physical Withering.
80-85% m.c
100%

STEAM AT 150 PSI

60-70% Rh

Hot air 25-30oc

At ambien temp.for cooling.

70-72%

Ambient temp.24-30oc dhool air for radiators

69-70 M.C. % cutting
o
temp 28-33 c

3
 135-160 mins at 24-28oc
Hot air at
145-160
o
c(Inlet)
And 75-90 oc
(Exhaust)

4
Electricity

en Leaf aterials.
2.8-3.2 at 80oc

25-30 mins (Drying)

Water

Steam Air
Waste ompost

nsport

PACKING OUT WEIGHT (KGS)

6
 PD 70-72 N/A
SORTING 5
 worked
s -done by a senior
officer manned by
trained guard,
documents made and
kept
-container verification done

Black tea Manufacturing Withering

 Prime object is to prepare the leaf for rolling by making it:
o flaccid
o permeable to juices
 Potential water loss for moisture contained in the tea leaves.


 The final mc closely controlled because of subsequent process (CTC) or rolling (physical
characteristics) for effectives of the process.
 Tea is spread thinly on tray banks or tats space 5-6 inches to allow free air access
 With alleyways to allow distribution and removal of leaf.
 This can be in open air or building.
 Open air has no control except you use hygrometric conditions of the ambient air.
 In closed building, air is circulated by fans; drawing air from bulking chambers.
  Humidity is reduced by mixing with hot air.
 Can be done using drum withering tats: perforated revolving drums holding 1500 pds which air is
blown (130 oF) and take less space.
 Realistic check on the % =out turn of dry to withered leaf.
 Light withers (40-42%), medium (45-50%).
 The average time is 18-20 hrs for tats and 3 hrs for drums.
 A leaf for rolling is prepared by making it flaccid and permeable to juices which rolling will
wring out and spread evenly on the surface.
 Take note of biochemical changes (after plucking enzymatic activity and soluble amino acids
increase for 20hrs and thereafter changes are erratic but caffeine increases for 72 hrs.).
 These occur whether the leaf is withered or not.
 Brings increasing permeability of cell membrane which mingling enzyme, polyphenols and oxygen
depends on orthodox manufacturing.
 The changes here increase quality eg
o Enhanced enzyme efficiency that promotes quicker and more efficient fermentation.
o Amino acids influence colour and aroma enhanced.
o Caffeine is a stimulant making tea desirable.
 Under-withering is not desirable because
o Leaf thrown out of rollers
o Juice may be expressed and lost.
o Wet leaves clog sieves of sifting machines.
o Produce flack tea of low specific gravity.
 Too much withering overtax the drier (firing) and stalk cortex removed from the rollers and tea
becomes more red and so more colour than quality.
Physical changes-physical withered
 Cell juice looses water first which is rapid then plasma colloids begin to loose water more quickly
 It is then followed with water evaporation resulting from changes
of plasma colloids which lose hydrolic nature.
 The cell protoplasm irreversibly looses its hydrophilic properties and leaf does not restore initial
turgor.
 The leaf becomes soft and elastic.
 The changes here are so obvious and profound that many experts have erroneously regarded the
withering stage as purely physical process attaching no importance to chemical changes.

Biochemical changes- chemical withered

 Enzymatic activity increases in the leaf required for fermentation 3 folds.
 Oxidation reactions:
o Involves oxygen absorption by the leaf
o followed by oxidative reaction within the leaf
o this confirmed by intensificationof colour of water extract of
withered leaf compared to fresh leaf.
o E.g if the colouration of fresh leaf is 100% then withered one will be 150-175%.
o Catechins vary considerably in withered leaf.
o Sum total in the plucked leaf 139 mg/g and withered one 116 mg/g.
 Changes in individual catechins in freshly withered leaf:
Catechins Fresh leaf (mg/g) Withered leaf (mg/g)
EGC 26.2 23.8
GC 13.3 11.1
EC 8.9 9.9
EGCG 72.2 54.7
 ECG 18.1 15.6

 The decreases in catechins with exception of EC seem to be associated with oxidative

transformation of the compounds.
 An insignificant increase of EC appears related to the degradation of EGCG which is also
suggested by increase in the content of gallic acid at withering.
 Increase of soluble nitrogen- due to changes in protein and amino acid composition in the tea
leaf.
 The activity of proteolytic enzymes increase resulting in protein hydrolysis.
 The content of soluble protein and free amino acids in the withered leaf also increases.
 The increase is 6-12 %.
 Biosynthesis:
o There is a significant increase in the content of free air
during withering.
o Amino acids not in unwithered leaf are present in the withered leaf e.g. leucine and
phenylalanine.
o It appears that biosynthesis of amino acids and other form of aldehydes and brown red
pigments in the course of oxidative interaction with catechins important for formation of
aroma and infusion of colour.
 Essential oils: marked changes develop.
 The biochemical process which results in the tea aroma during fermentation starts at withering and
that is why you can smell the fruit aroma in withering room.
 Withering process characterized by accumulation of appreciable amount of essential oils
responsible for the specific tea aroma e.g linaldehydexide, nerd, benzallelyde, trans-2-hexenol, cis-
3- hexenol.
 In some studies green and withered leaf were found to contain 0.3-0.5 % essential oils respectively

Degree of the wither

 This is the extent to which withering process proceeds and may be expressed in 2 ways:
i) Weight of leaf withered as percentage of fresh leaf weight
= withered wt/fresh leaf wt x 100. This compares processes/operations on day to day
basis. But doesn’t account for moisture content due to weather, therefore not reliable.
ii) Out-turn of the black tea= wt made tea/wt withered tea x
100. It is reliable since variation of moisture content of made tea is very small (2.5-3.5 %)
if dryer properly constructed with correct through-put and airflow, temperatures
maintained. It is used to control drying process. 40-42 %= light withered, 45-50
%=medium to hard wither.
Withering systems
 Natural withering
o air in natural circulation is used and no control of speed, temperature or rh.
o Open sided shade is normally used.
 o Tea leaves are placed on series of floors usually wire supported large mesh wires netting
covered with removable hesion cloth.
o It results to potential water evaporation from the tea leaf and biochemical and physical
changes. Requires large space/area.
o Has many uncertainties: rate of moisture loss depends on natural conditions, rh, rainfall
and wind speed.
 Controlled withering
o Air temperature is controlled particularly where heating is done.

o Withering is more efficient and more uniform not just within a particular path of tea leaf
but from day to day.
 More uniform product quality with mc etc. can be:
i) Tunnel withering
o Tea leaf is spread on layers of trays on the mobile trolleys hession or wire netting.
o The leaf loading on the trays is about 1.8 kg/m2 the trolleys are wheeled into a
withering tunnel and subjected to warm air through tunnel, typically air mass at
speed 2.5 m/s and has wet bulb depression 7.5 oC (no relative humidity).
o It is difficult to estimate the dry bulb temperature and this can say something about
rh.
o The warm air should not exceed 38 o
C.
ii) Trough withering
 It is the pre-dominantly used in Kenya in all factories.
 Much longer and narrower 25m.
 There is a wire, hession, nylon netting fixed horizontally on the upper part of the tough
about 9 inches below its top.
 A layer of tea leaf, 8 inches (20 cm) thick is spread on the netting resulting in a loading of
about 23.5 kg/m2.
 At the bottom of trough is tunnel which serves as an air condition.
 Air is circulated by a fan made of steel tubes through which steam flows and condenses as
it looses heat to the surrounding air.
 The condensate is re-circulated back to the boiler via steam trap (prevents escape of live
steam and allows flow of condensate).
 Indirect fuel heaters may be used (100-industrial diesel oil) especially at KTDA for 1o-15
years.
 Hot air temperature should not exceed 38 in the troughs. The air fan usually reversible (air
flow direction can be reversed).
 Withering usually starts with ambient air flow in downward direction through the leaf.
 This is done mainly to remove leaf mc.
 After 2 hrs the flow is reversed, air moves through the heater and upwards through the bed
to the leaves. Warm air flows upwards through the leaves 15-18 hrs.
  The total withering time varies from 18-20 hrs in normal practice.
Withering here takes much space and capacity of the factory, better improve withering
time to increase capacity.
iii) Continuous withering machine- this is an option to be considered but not well adopted
in Kenya. Long used in Russia.

Drawing

Tea leaf spread on perforated trays move from feeding end of the bed to the delivery end where leaf
is discharged onto a conveyor belt to rolling area.
 Warm air flows upwardly through the bed of withering leaf and there is continuous
feeding and delivery to the moving belt.
 The belt speed is variable and operation can determine withering time from one end of the
belt to the other.
 It is improved with continuous flow compared to the other types where you wait for rotors
before the next step.
Factors affecting withering of tea leaf
i) Extent of tea damage- damage tends to cause premature critical changes and hence
uneven withering. There is deterioration of leaf appearance and liquor quality if damage is
significant.
ii) Type of leaf received- course plucking results to slow withering leaves than fine plucking.
Leaves from different yields may have different sizes and composition which may influence rate of
withering (physical and chemical changes).
iii) Moisture content of leaf surface- surface water content determines degree of withering or
time. Its presence encourages bacterial growth which adversely affects final tea quality.
iv) Thickness of spread- for given withering trough, design of pan determines speed of
withering. Air flow rate depends on thickness of spread of leaf, if thick requires higher air flow
rate and hence affect degree of wither and increase time of wither.
v) Drying air parameters- drying capacity of air is influenced by temperature, rainfall, air
flow rate. If air is saturated (100% rh), no evaporation of water will be effected from the leaves.
The lower the rh, the higher the rate of withering. Temperature
affects rh, rh decreases with its increase and vice versa. Increasing it means high evaporation rate
since air has higher holding capacity for water. The flow rate determines how much water is
evaporated at a given time from a batch.
vi) Duration of withering- influences quality, high for long wither and v.v. usually takes 18-
20 hrs in Kenya but can be shortened to 6-8hrs with proved sufficiency to allow chemical and
physical changes to have high quality.

Rolling
 The object of rolling is to macerate the leaf so that the enzymes and their substrates get intimately
mixed up.
 This is achieved mechanically either by the use of an orthodox roller, the rotorvane, or by CTC
(crushing, tearing and curling) machines.
 Rolling ruptures the cell wall thereby enabling the production of enzymes.
 Essentially macerated and formed into particular shapes.
 In the cut tear and curl system they are curled. Methods:
a) Orthodox method
 Orthodox tea- tis distinct and demand by some markets.
 It uses pressure rollers and is batch process where withered leaf (55-60 % mc) is
fed to rollers of vertical metal cylinders open at both ends.
 The lower end rests on larger circular table fitted with series of ribs and battens.
 The fittings are basically protrusions into the leaves.
  The upper ends of the cylinders are closed cup which compresses the leaves-
drawing.
 The roller is rotated over a table surface at a speed of 40-75 rpm.
 Some designs may have rotating tables-double action rollers.


 The rolling cycle takes 30 min and leaf discharged and passed through a screen and
larger pieces recycled back (feed roller)

 Twists leaf, breaks it and expresses juice.

 Compress and turn leaf over, keeping it in continuous motion (like rubbing between palms)
 Work done depends on pressure, friction between leaf and rollers and motion (speed throw
of crank).
 Leaf bruised and twisted (raised battens-can be smooth or has cutting edges set at angles)
depression, and rounded off cones.
 Under high pressure and severe battens, leaves tend to disintegrate. Without pressure, action more
directed towards wringing and twisting.
 The juice is expressed from leaf and spread as thin film on their surfaces (liquids forced out of
cell without rapture) ad mix catechins and enzyme which were separated and exposed to
atmosphere.
 Thus enzyme oxidation of catechins begins.
 The green colour diminishes and brown or coppery colour begins to appear.
 Thus rolling affects final tea and has to be arranged well since:
o At onset, evolution of heat generated by friction forces and exothermic chemical
oxidation.
o The rise in allows fermentation but not be too high (80-90
o
F)
o Pressure by consolidating leaf confines and accumulate heat. Pressure and battens impede
circulation of leaf and prevent constant air interchange within this mass.
o Thus if pressure is too high, may rise too high and cause insufficient oxygen.
 o Number of times a batch of leaf is rolled varies with tea type, degree of wither or rolling.
o If light wither then a few times (3-5 rounds).
b) Legg-cutter (machine)
- It was originally designed for tobacco cutting and combines leaf into firm cake and cuts it into
strips varying in width ¼ -1/10 inch (0.625-0.025cm)

- The strips are then given short light roll in roller with a flat table and centre concentration.

- Not adequate when used alone but combined with pressure rollers therefore used as pre-treatment.

- Has advantage that unwithered leaf can be processed without difficulties. Numbers of rollers
required may be about 1/3 of those required by orthodox method.

c) Lawrie Tea Processor (LTP)

- Modified hammer mill with barrel containing shaft carrying a series of knives and beaters.
- Shaft rotates at a high speed while leaf blown into and discharge from machine by means of
centrifugal fan.
- Advantages include:
 low capital required,
 low maintenance cost,

- Main disadvantage is that it can only be operated satisfactorily over very narrow range of low
moisture content (70-72%).
d) Rotorvane machine (RVM)
- Consists of horizontal cylinder fitted with rotor assembly which include a worm to drive the leaf
forward.
 Series of vanes which squeeze the leaf against battens and indentations inside barrel of
machine.
 Gap through which leaves discharge and adjustable to allow for pressure applied to the leaf be
varied.

Diagramme

- The machine can be used as the only means of rolling leaf.

- In this case 2 or more machines of different diameters may be used in series and course materials
recycled.
- Alternatively, a RVM can be used to provide pre-treatment for CTC.

- For pure RVM manufacture mc of 65% is required

e) Cut Tear and Curl (CTC) Machine
- Consist of a pair of horizontally mounted stationary steel rollers rotating in opposite direction.
- Surface of each roller has series of teeth engraved on it.
- The rollers are mounted in such a way that the teeth mesh together and the gap between them
adjustable.
- 1 roller runs 700-1000 RPM and the other at approximate 1/10 of this speed 70-100 RPM.

- The withered leaf first preconditioned by processing in RVM or other suitable alternatives then
fed onto surface of slow moving of the 2 CTC rollers.
- Usually 3 CTC machines are used in series with gap between rollers being progressively reduced.
Recommended mc of leaf 67-72%.
- Moisture Content determines amount of heat generated during cutting (if drier more heat and vice
versa).
- Maintenance of CTC rollers include periodic sharpening of the teeth with special machine (after
100 hrs operation).

Comparison of various rolling methods

1) Leaf appearance- pressure roller is favoured where appearance is of prime importance.
- Its best grade is relatively larger pieces of leaves, black with definite twist imparted

- RVM can produce similar style leaf but small pieces.

- CTC grades are even and graining and generally smaller with narrow particle size distribution.

- LTP usage results in a product somewhat similar to CTC but rather broader particles size
distribution.

2) Rate of fermentation
- Rate of reaction increases as particles of macerated leaf reduces in size thus CTC teas are
fermented about 11/2 hours, pressure rollers 2-3 hours.
- The rate limiting step during fermentation is diffusion of oxygen to the reaction sites within leaf
particles.
- Smaller or particles that have larger surface area: volume ratio and allow oxygen transfer faster.

- Pressure roller and to less extend RVM compress the leaf and restricts oxygen transfer to interior
of particles. This effect is minimal in CTC or LTP rolling.

3) Liquor quality
- Liquor from CTC teas tend to be strong and brightly coloured
- whereas liquors from pressure rollers are generally thinner and less coloured but often superior in
flavour due to the following reasons:
i) The more complete oxidation of volatile precursors especially area of unsaturated fatty acid
lead to high levels of less desirable volatile substances during fermentation of CTC rolled
teas.
ii) Some desirable volume substances are destroyed by oxidation during fermentation of CTC
rolled tea
iii) Where pressure rollers used the relatively anaerobic conditions created within compressed leaf
allows the glycoside enzyme
 responsible for the release of the desirable volatilise: linalool and geraniol remain active for
long period resulting to high levels of them.
iv) Due to the high moisture content of CTC rolled teas and the larger surface area of the leaf
particles, there is greater opportunity for loss of desirable volatile substance during drying.

Roll- breaking and Green –leaf Sifting

 On discharge from roller leaf mass is more or less compressed into lumps, broken in sifting (in
rectangular or sieve set on moderate mechanical agitators.
 Roller discharge is fed into chopper with revolving beaters to break up the mass before falling to
sieve for the next stage.
 Roller breaker and green leaf sifting performs 3 essential functions:
i) Cools heat to prevent retention of any excess.
ii) Aerates tea mass.
iii) Separate leaf to portions uniform for fermentation (feed continuously spread in sieve).
These now form dhools.

FERMENTATION
- Critical process that if not properly done may lead to quality impairment.

- Involves a series of complex reactions of polyphenols, enzymes (polyphenoloxidases,

orthodiphenol oxidases or catechol oxidases) and oxygen.

- Complex series of oxidation, chemical reactions some of which are not fully understood but
major steps seem to be known up to now.

- Main chemical reaction involves enzymes naturally present in tea leaves.

- Hence withering temperatures have to be low so as not to reduce the quality of the enzymes
responsible during fermentation.
- During fermentation there are wide varieties of chemicals responsible for
colour, taste and flavour of the final tea.
- It is a critical stage with regard to tea quality.

- Fermentation has to proceed to optimum level so that we have optimum quantities of desirable
chemicals and minimize quantities of undesirable chemicals.
- Once optimum levels are reached fermentation reaction has to be quickly stopped (by drying).
Consider the chemistry of tea leaf Enzymes:
 Oxidation enzymes of tea polyphenols occur on exposure to air.
 Thus use of oxidase enzyme with Cu as prosthetic group with both soluble and non soluble
components.
 It is specific and oxidises hydroxyl group in ortho-position and the rate of oxidation depend on
the amount of enzyme and accumulation of fermentation products.
 The activity is high in dry weather.
 Peroxidase oxidises catechins but play no role in fermentation.
 Pectin broken by pectinases during manufacturing.
Vitamins:
 Riboflavin (B2) - Persists up to storage.
 Ascorbic acid oxidised on manufacturing during fermentation (black tea)
Carbohydrates
- Starch and sugars

- Inorganic constituents
-Mainly as salts in cell sap:
a) Aluminium
b) Manganese- gives green tint of leaf. Concentration increases with leaf age.
c) Potassium- Highest among the mineral constituents and richest in young foliage.
d) Calcium- second most abundant mineral.
e) Mg
f) Iron- variable and low if Mn is high.
g) Copper- Important because it plays a role in fermentation
h) phosphorus-high concentration in young leaves.
Fermentation process
 It is the process of oxidation of leaves.
 The mechanical aspect involves spreading out of the leaves macerated by rolling a layer (dhools)
5-8 cms thick,
 For 45 minutes to 3 hours, depending on the quality of the leaves.
 Fermenting machines make the process continuous, that is, every unit of macerated leaf has to be
spread out for individual treatment.
 The thickness of spread takes care of oxygen access, rate of moisture loss and leaf temperature.
 Requires good air circulation.
 If hot climate kept humid by reducing temperatures in controlled fermentation rooms
 Leaf changes to coppery red shade and looses grassy oduor and then to dark colour and pleasant
aroma develops.
 Time must be kept from rolling and be limited for after 4 hrs there is loss of quality.
 If leaf colour (green) is retained after this, then it means rolling was insufficient.
 Over-fermentation decreases quality but increases colour (dark).
 Daily washing of fermentation trough surfaces to remove juices which may be sources of bacteria
is required.
 Dhools are then transferred to driers for firing.

Fermentation products:
 Most chemical processis oxidation of polyphenols by atmospheric oxygen
with help of oxidase.
 Results to production of o-benzoquinone derivates from catechins.
 Individual phenols oxidized successively.
 The catechin derivatives only 2 are important- epigallocatachin and its gallate.
 3 variants formed: ECG, EGCG and hybrid of EGCG and EGC.
  The primary results of oxidation are the o-quinones that are highly reactive and undergo wide
range of different reactions plus oxidation of other substances.

 The rearranged pairs are bisflavanols which are capable of further reaction with ortho-quinone
already present giving theaflavins (TF).
 An additional oxidation not enzyme controlled transforms theaflavins to thearubigins (TR).
 The reaction does not proceed to completion during normal tea manufacture and finished black
tea contains both TF and TR and TF decreases with prolonged fermentation time.
 Orthodox methods of rolling gives lower TR/TF than maceration.
 Oxidation leads to disappearance of the bitter taste of unoxidized tannins and development of
pleasant tender and astringent taste.
 Complete chain:
GC/catechins + oxygen
 Enzyme oxidation
Ortho-quinone

Condensation with Amino acids

Paired dimerization Bis-flavanols

Condensation with o-quinone Theaflavins

Non-enzymatic
oxidation Thearubigins
 Bisflavanols are formed by condensation of 2 molecules of 0- quinones derived from GC and are
colourless.
 TF results from oxidative condensation of one molecule of the o-quinone derived from EGC or
condensation of bisflavanols with o-quinones.
 They influence quality of teas-if high then higher quality. Their formation is favoured by
availability of oxygen and sufficient polyphenol oxidase and high levels of sufficient substrates.
 The EGC levels in fresh tea has been found to indicate the extent of theaflavin formation on
fermentation and the ratio of GC:C is very important in determining the potential for theaflavin
formation.
  Thearubigins are coloured phenolic oxidation products and are a mixture of various compounds
(polymeric and non-polymeric).

Kinetics of formation of theaflavins and thearubigins

 Temporary oxygen starvation at the start of reaction lags the formation of theaflavins.
 The formation then proceed at a steady rate reaching peak corresponding to the consumption of
almost all the available flavanols.
 Oxygen consumption then slows down markedly at this point and subsequently theaflavins
decrease slowly.

 Drawing.
 Thearubigins are rapidly formed and steadily from the onset and continue to be formed slowly
after theaflavin peak has passed. Polymeric thearubigins are formed only very slowly at fast then
increase fatster after theaflavin peak has reached.
Factors affecting the formation process
i) Oxygen supply-should be adequate for the formation of o- quinones and theaflavins
ii) Temperature- maximum theaflavins are obtained at low temperatures.
High temperatures encourage oxidative polymerisation leading to reduction in theflavin
and increased polymeric thearubigins due to 2 reasons:
 High temp results in increased activity of peroxidase believed to mediate in
conversion of theaflavins to polymeric thearubigins,
 it also results in reduced solubility of oxygen in the leaf juices hence less available
oxygen
 iii) Time- should be up to just peak of theaflavins. Normally subjectively judged by
appearance and aroma of fermenting leaves:
 Green yellow yellow/brown light/brown coppery red.
 At low temp the time does not need to be controlled very precisely but as the temp
and reaction ratios increase, control of fermentation time is much more important.
 It varies from 45min t0 3 hrs depending on the temp and type of processing
equipment.
iv) Degree of wither-the amount of TF formed decreases with increase of the degree
of wither. Possibly 2 reasons:
 activity of polyphenol oxidase decrease with increase of the degree of wither,
 Greater heat generated on maceration of drier leaf leading to more rapid rate of
reaction but low final levels of TF due to competing influence of temp.
v)PH—the initial PH of leaf juice is about 5-6 but falls during fermentation to 4.6.
Adjustment of PH to 4.5-4.8 prior to commencement of fermentation increases TF and
decreases TR thereby improving the products.
vi) U.V Radiation- exposure of leaf to uv accelerates the rate of reaction, increases
levels of TF and this improves blackness of final product.
Other oxidation reactions
 The o-quinone act as oxidizing agents are themselves reduced back to flavanols.
 Some of the reactions are significant in determining the composition of the volatile fractions and
hence tea aroma.
 They include oxidation of amino acids, unsaturated fatty acids and carotenes:
i) Amino acids- oxidative deamination yields corresponding aldehydes with loss of CHO &
NH3.
R.CH2 (NH2).COOH O2 R.CHO + CO2 + NH3 (STRECKER

DEGRADATION) .
 Some of the aldehydes are significant flavour compounds
e.g. formation of phenyl acetaldehyde with rose-like aroma from phenylalanine.
ii) Unsaturated fatty acids- oxidation yields aliphatic aldehydes and acids of lower
molecular wts
 e.g. oxidation of linoleic/linolenic acids giving rise to trans-2 hexenal, hexanoic acid and
trans-2-hexenoic acid.
iii) Carotenes- terpenoids, aldehydes, ketones which are important in black
tea aroma are formed on their oxidation.

N/B:
 The other enzymatic reactions on fermentation:
  Polyphenols and oxidative products are powerful enzyme inhibitors and seems therefore most
enzyme systems in the leaf cease to function at or soon after maceration.
 But some enzymes other than polyphenol oxidase and peroxidase do survive e.g.
i) Relatively large amounts of methanol in unfired leaf results to activity of pectin methyl esterase
(dimethylated pectin).
ii) Chlorophillases – injured leaf after pruning does not show any green pigment since initial stages
in the breakdown of chlorophyll are enzyme mediated. It is likely that these enzymes also survive to
some extent and contribute to appearance of final product.

iii) Glycosidase- some volatile substances that are significant in flavour determination such
as linalool and geraniol are present and also glycosides in the intact leaf are released during maceration
which apparently as a result of enzymatic action.
Fermentation methods
i) Floor fermentation
 Cut rolled leaves ‘dhools’ are spread on the floor at a layer sufficient to allow oxygen to diffuse
throughout the mass (1-2 cm thick).
 Heat of fermentation is absorbed by the floor and frequent air humidification done to prevent
leaf surface from drying.
 Disadvantages: require large floor surface, unless floor is clean and smooth there is danger of
building bacteria whose role may lead to unpleasant taints in the final product.
ii)Tray fermentation
 Leaves are spread on trays which are then packed on mobile frames in fan room.
 Trays may be stack in layers and each rack gives total fermentation space of 9 m2 and leaf
thickness of 4 cm.
iii) Tubs-trolleys
 Most pre-dominant in Kenya.
 Small mobile tubs supporting bed of leaf 20-25 cm deep on a wire mesh.
 The tubs are connected to supply of humid air which enters the base and moves upwards
through the leaf bed.
 Theleaf raked from time to time to minimize uneven fermentation
due to temp variation with the leaf bed.
Drawing
iv) Continuous fermentation Unit (CFU)
 Continuous leaf flow from rollers into fermentation unit and firing.
 KTDA have both the tubs and CFU. The leaf is spread on perforated belts or trays and
continuous airflow through leaf is supplied.
 Fermentation proceeds as the leaf moves on belts.
 Often stacked belts with intermediate ball breakers are used and more than one belt is used.
Disadvantages:
 Expensive especially capital cost and running costs.
 Difficult to maintain compared to tubs
 Difficult to clean.

Advantages:
 Minimal space required
 Provision of continuity in production process once the leaf is fed.
FIRING/DRYING
 The process during which the enzyme activities are stopped
 Moisture content is brought down from 45-50 % to 2-3 % in dried black tea.
 It also allows development of black tea aroma
 Physically achieved by blowing hot air through fermented leaves as they are conveyed in chains.
 The drying process lasts for about 20 minutes.
 Drying in steps till last (bottom trays) or on fluidized beds.
 The hot air is provided for by furnace or steam boiler through passage tubes.
 Induced drought is maintained by fans.
 Dhools fed into a hopper ancillary to which is an automatic spreads.
 There are automatic thermometers recording inlet and outlet temperatures.
 Subject to temperatures of 140 C< in dryers. There are 3 stages:
o

1. Chemical changes take place during drying which are very important for quality of the
final product.
 2. There is colour development.
3. Dried tea particles come out of dryers which vary widely in sizes.
 It subjects fermented tea to forced blast of hot air in such manner that hottest air comes
first into contact with driest tea.
 Through water evaporation fermented leaf looses coppery red colour and transforms to black
tea.
 At commencement fermentation proceeds at accelerated rate.
 Enzyme activity declines steadily and only ceases all together when moisture content falls to
about 20 %.
 Time taken to reach this point is critical:
o If drying is too rapid the outer layer of the leaf particles or agglomeration of leaf particles
will harden and prevent diffusion of moisture within.
o If too slow the period of high temperature fermentation will be too long and unpleasant
taste develops and tea is said to be stewed.
 Precise temperature time regime is less important once enzyme activities have been
completely arrested but it is desirable that leaf reaches highest possible temperature consistent
with avoidance of burnt taste.
 This ensures maximum possible enzyme inactivation.
 The typical drying temperature ranges 100-150 oC at the start and low temperatures used as
the end of leaf temperature approaches air temperature.
 Low temp is sometimes employed with object of retaining high proportion of flavoury
volatiles.

Chemical changes during firing

 Arrests enzymatic activities and consequently biochemical processes.
  Large proportions of essential oils formed on fermentation are volatilized (75-80 %).
 Practically every fraction of essential oils is reduced.
 Total acids increase.
 Quantity of nitrogenous compounds is reduced.
 Methanol content reduces as it is volatilised (formed after fermentation due to demethylation
of methyl) thus decreased toxicity.
 Heat sensitive vitamins e.g. E are lost.
 Contents of glucose, sucrose and starch decrease insignificantly which is very important for
good quality since firing results in specific tea aroma due to partial caramelisation of soluble
carbohydrates.
 At high temperature fermented tea leaf undergoes certain transformation leading to typical
lactic acid aroma and contents of many compounds determining aroma increase e.g. alcohols,
aldehydes, acids.
Tea driers
Tea drying is predominantly done on fluidized beds but 15 years ago it was done on endless chain driers.

1. Endless chain drier (ECD)

 As stacked bed continuous fermentation unit without ball breakers.
 Used in series of slowly moving perforated belts of trays placed above each other.
 Fermented tea is fed at one end and falls and moves to the other end where it falls to the
next lower level of the belt.
 The process is repeated till tea is discharged at the end of the lowest belt.
  Heated air is fed at the bottom of stacked belts and flows upwards through tea leaf and
discharged to the atmosphere after the top tea.
 Counter current occurs with driest tea leaf at the bottom belt in contact with hottest
incoming air and moist tea leaf on top belt contact air of lowest temperature.
 The stack belt thus is like black box giving counter current but also cross-flow.
 Drying temperatures were in the region of 104-110 C and some literatures indicate low
o

temp of 82-94 oC
2. Fluidized bed driers (FBD)
 Layer of tea in the drying chambers is fluidized by passing hot air through an upward direction.
 There is intimate contact between air and leaf particles resulting in efficient uniform drying.
 2-3 drying sections each with own air supply.

- Tea leaf
out

Tea lea

Hot air in hot air in through the tea leaves

 Fluidization due to upward air movement through the bed into the tea particles.
 The leaves are not stationary and do not rest on each other but move continuously on suspension.
 It is very important to control air velocity.
 At very low velocity no fluidization and beyond high limit, particles are carried away.
 Thus minimum and maximum limits of velocity are observed.
  There is always entrainment of particles. Air passes through cyclone which separates air from
tea leaf particles.
 Air heating is usually done by steam but is the same as endless chain drier
 Drawing
Advantages
 Few moving parts hence low maintenance costs
 Produce cleaner tea with less fibre and more grainy as fibre is entrained by air.
 More surface area of heat and mass transfer therefore more efficient drying.
Disadvantages
 May be tendency to stewing in entirely stages where thick bed not fluidized and heat transfer is
poor.
 The leaf is moved through machine by air flow with mechanical aid consequently precise control
over residence time not possible and particles are unevenly fired. Particles taking too long may
over dry and have poor quality and vice versa under dried.
 Very high air flows required for fluidization may result in greater loss of volatile substance than in
tradition ECD.
SORTING AND GRADING
- Tea from drier is a mixture of fibre and tea leaf with broad particle Size distribution to be
separated into sizes.
- Fibre extraction– sorting by means of PVC coated rollers.
- Sketch

- Friction causes the surfaces to acquire electrostatic charges which attract fibre and attached
as tea moves along belt.
- Fibre is removed from the belt.

- Grading- by screening: series of screens of different of different sizes with one largest and the
bottom smallest aperture.
- Whole unit vibrates ( vibro screens ) separates to 4 grades:
i. BP1-Broken pekoe 1
ii. PF1- pekoe fanning 1
iii. PD1- pekoe dust 1
iv. D1- Dust 1

Diagram:

These are primary grades

- The rollers have on the surface trapped fibres with some tea.

- They are swept and taken back to sorting line same way to give secondary grading same way.

- Further sweeping and back give another grade, “ fanning” and

the sweepings give broken mixed fanning ( BMF )
Packaging
- In factory for export and local packaging industry, not for consumers.

- Can be blend on requirement.

- Pure grade is rare in the market.
 - To minimize water vapour since tea is hydroscopic.
- Flavour retention very important: Use paper sack for export.

- 4 layers Kraft paper lined with Al foil normally used.

- Tea sold to packers in canvas bags lined with polythene sheet.
Tea Tasting
- Quality control involves:
- Looking at tea leaf particles as they appear (dry tea, black or brownish.
- Cleanliness: (fibrous or dusty), even, twisted, curled or desired.
- Infused leaf (after extraction) colour, dust, brightness, is colour mixed or one type.
- Taste of liquor: taste, colour, body (thickness) and flavour.
Instant tea manufacture
- Teas soluble in hot and cold water

- used in some countries as ice tea mixed with other ingredients

e.g. cold lemon tea mix which has sugar, citric acid, natural lemon flavour and tricalcium
PO4.
- Processing operations include:
Selection of raw materials
- Black tea fermented and dried leaf, oolong or green tea i.e. uses finished products of primary tea
factory.
- Choice made on:
 Processing requirement
 Market tea intended for
 Commercial restriction on manufacture
Extraction:
 Use of water solution compounds by extension liquid (water recycled).

- Final concentration of water fairly low by 3-5 % TS.

- Can be batch or continuous

- Batch- use extension tanks and water at 80-900c. Tanks remain stationary but extraction liquid
moves from tank to another.
- Extraction continues for some time and tank emptied before introduction of fresh leaf.

- Continuous more convenient e.g.

Counter-current continuous extraction

Diagram

-tea leaves introduced at lower end and conveyed upwards by rotation of screen while extracting
water flows in reverse direction.
- Soluble solids transferred from leaves to water.
- The screws perforated to allow water flow more easily through tea body.
- Extraction temperature controlled by series of heater on the body of the unit.
Aroma stripping
Extraction results in loss of aroma compounds therefore need to retain.
- Vapour which aroma compounds condensed (dilute aroma) hence concentrated by
refractionating column.
- Aroma comes top as vapour and is condensed.

- Some aroma taken back to distribution column to aid it reflux but the rest taken to storage tank.

- Reflux ratio= 20:1 (storage: tank)

- The distillation column has 2 fractions (top- aroma concentrate, bottom is water with some aroma
compounds which form part of extraction liquid in the extractor.
Concentration
- The dearomatized extract from the separator is evaporated by steam heating.

- Vapour concentrated mixture goes to separator (separate to liquid and vapour) and

- liquid is then concentrated and taken to storage tank as aroma concentrate.

- Part of concentration is further concentrated.

- Vapour fraction from separator is mixture of vapour and aroma compounds.

- Thus dearomatized extraction has some aromas condensed in 2 stages.

i. Using ordinary water and condensate forms part of extension liquid in extractor.
ii. Vapour fraction from separator (those not condensed in first condenser). It is a refraction
condenser using chilled liquid to condense aroma compounds.
- Condensate taken to storage tank and part of it joins dilute aroma on its way to distillation
column.
- Concentrate plus aroma concentrate and part of aroma condensate are stored
together.
- Corn syrup solids usually added to these concentrates before drying to retain as much aroma
compounds as possible.
- Drying also results in loss of aroma due to evaporation.

Drying- 2 methods commonly used:

i. Spray drying- mostly
ii. Freeze drying- more expensive. This tea is more expensive, high quality due to superior
reconstitution ability.
Packaging
-instant tea powder has MC 3% but very hygroscopic and absorbs moisture if exposed on air to unsafe
levels. Ensure minimal entry of water by always tinning.
N/B:
Cream processing - Done only when tea is subjected to temperatures below 6 0c. Thus avoided by not
cooling to these low temperatures, which turn extract into cream of opaque brown colour which gives
non uniform product. It is processed especially alone before concentration.

Quality Questions

 Quality is determined by many factors (controlled and uncontrolled)

 Biochemistry researches determine constituents that promote good quality.
 Ethyl acetate dissolving substances indicate quality produced by efficient fermentation.
 For good colour TR/TF should be fairly Ltd (at best 10-12 range) by regulating fermentation
time and method since TR is 10*
  Prime consideration of quality is nature of plucked leaf, good leaf of high polyphenol content,
high enzyme activity, physically allows tissues to be worked on.
 Thus course plucking results in poor quality tea because of
- Low average polyphenols

- Mature and more lignified leaf not easily macerated and cells distorted giving free access to air on
fermentation and contains enzymes mingled with polyphenols
 Rhythm of growth of tea bush affects quality e.g. Quality improves with age after pruning
up to 4 years.
 Damaged leaf not good due to uncontrolled fermentation.
 Slow growth results to high quality
 Long withering increase bacteria which is not required Finished tea should have 3 %mc
and since they are hygroscopic will pick moisture if not controlled (9-10%) mc encourages moulds giving
musky taint to the dry liquor
Healthy benefits of tea
- Body protection against heart diseases, stroke, cancer and more Why?

- High levels of antioxidants (polyphenols, flavonoids and catechins) they scavenge

radicals.
- Fluoride benefits teeth and has antibacterial properties controlling bad
breathe and formation of plague.
 White tea has more antioxidants than all.
 Green tea has more catechins than black.
 Unfermented has more polyphenols.
 Brewed (caffeinated) has more antioxidants. Tea drinking
has the following benefits:
- Low blood pressure.

- May lower the cholesterol level therefore reduce chances of heart attack.